In mining and tunnel construction, the tunnels generally are formed by means of drilling or blasting, or with the aid of various types of cutting machines. During such tunneling it is often unavoidable for the working faces to become larger than the useful and/or desired cross sections, especially in cases where the rock being worked is not compact. Therefore, for reasons of safety and in order to maintain the predetermined useful cross section, the driven tunnels generally are provied with a support or lining. When such supports are utilized it is necessary for the hollow space between the elements of the support and the solid rock of the working faces to be filled in, in order to prevent rock movement and to transfer the rock pressure evenly to the support.
The filling in of the hollow spaces between the working faces of the tunnel and the support may be accomplished in a variety of ways. For example, after a support has been constructed from sheathing of timber, metal sheets, meshed wire, concrete slabs or the like, the hollow space remaining between the support and the working faces of the tunnel may be packed with loose rocks obtained during the tunneling operation. Another known technique comprises filling the space between the sheathing elements of the support and the rock face with concrete or some other quick setting building material. Still another technique, known as the Torkret process, requires less of a material expenditure and merely comprises the application of a several centimeter thick layer of sprayed concrete (gunite) to the rock-face of the tunnel after blasting, whereby the inherent bearing strength of the rock is increased.
According to a more recent technique, plastic hoses are inserted between the rock face and the sheathing, which in this case consists of meshed wire mats disposed on timber support elements. A liquid plastic foam material is then pumped into the hoses and permitted to solidify. In this manner the hollow spaces between the rock face and the support are filled with a cushion formed by the foam-filled hoses.
The demands to be made of this foam-filled hose cushion however, are extremely critical. First of all the hose must be made from a material which can satisfy the requirements for the protection of the miners, for example, with respect to flame resistance and electrical conductivity. The hose material also should be harmless with regard to the health of the miners; for example, it should not result in the formation of any harmful decomposition products. The hose material, furthermore, must have a capacity for extension such that the cushions, developing during filling, will completely fill all hollow spaces, thereby preventing the escape of any accumulations of mine gasses, which escape from the rocks. In addition, the hose material must exhibit an acceptable ductility and tear resistance so that the hose will be able to absorb an operating pressure of at least about 5 bar without tearing. The hoses must also exhibit a resistance to piercing which is as high as possible since the hoses are to be used in conjunction with sheathing of wire or the like which often contains projecting points or edges. At the same time, a high strength against continued tearing is desirable so that minor damage to the skin of a hose will not become the starting point for extensive tears. Finally, one should expect from the hose material, that it will hold the compressed plastic foam together so strongly, that the resulting cushions, despite the relatively low resistance to pressure of the unsupported plastic foam, will absorb relatively high pressure loads and will be capable of transferring such loads to the tunnel support. The hose materials used in the prior art have not fulfilled the above noted requirements, or at least not all of them.